The long term objective for this project is to understand the regulatory mechanisms and specific mediators of innate antiviral responses in human lung cells following influenza virus infections. Much is known in general about cellular virus detection by the innate immune system and the inducible gene expression events that accompany the acquisition of cellular and systemic responses. However, individual hosts can demonstrate variability in resistance to infection in a virus-specific or cell-specific fashion. These differential responses are the result of many factors including variable transcriptional responses or post- transcriptional regulation of gene expression at the primary site of infection. This application is designed to elucidate new paradigms for innate cellular responses to influenza virus infection with both basic research and clinical approaches. One specific aim will examine the hypothesis that post-transcriptional gene regulation modulates canonical antiviral gene expression programs during influenza infections, and will decipher the roles of cytokine- and virus-induced microRNAs by examining their biogenesis and activity in infected lung cell lines. A second aim will test the hypothesis that differential gene expression in the airway mucosa, the main site of influenza virus infection, relates to severity of clinical presentation of human influenza. Transcriptomes of airway mucosal samples will be analyzed during acute phase and convalescence of human influenza infections to identify novel gene expression patterns and pathways related to severe influenza infections. In addition, comparison of airway mucosal transcriptomes between those predisposed to severe influenza and those who experienced milder disease will identify novel gene expression patterns and pathways related to susceptibility to influenza infections. Together these aims will elucidate new fundamental innate immune mechanisms, provide a more sophisticated understanding of the antiviral response, and potential new targets for antiviral therapy.